1. Field Of The Invention
The present invention relates to cooling assemblies for air-cooled electromechanical devices and in particular, methods for making such cooling assemblies for such devices.
2. The Prior Art
It is well-known that there is an optimum temperature range of operation for devices which perform work, within which the thermal efficiency of the device is highest. When the device, be it electrical, chemical, or mechanical in nature, is operated outside this optimum temperature range, its thermal efficiency falls and, especially at higher temperatures, the failure to dissipate enough heat can cause structural stresses in the device due to uneven, non-uniform temperature gradients. In the extreme case, such stresses may result in device failure.
In particular, ion gas laser performance is extremely sensitive to heat build-up and an uneven temperature distribution. Uneven temperature distribution in ion gas lasers can cause mirror instability and stress fractures in the structure of the laser tube itself, causing total failure. Therefore, there exists a need for efficient methods of heat dissipation for electromechanical devices such as ion gas lasers.
Liquid cooling is well-known in the art as one of the most effective methods of dissipating heat. However, the cost of liquid cooling can become prohibitive due to the complexity of sealing, pumping, circulating the coolant, and dissipating the heat absorbed. Air-cooling is a less expensive alternative and may be used when temperatures generated are not relatively high and the device from which the heat is to be removed can withstand a higher equilibrium operating temperature and/or the physical size of the device is relatively small.
Air-cooling can either be convection or a forced air type. Convection air-cooling relies on the still air to absorb the unwanted heat generated by the device which is then removed by convection currents. Forced air-cooling, on the other hand, is more effective because it relies on the forced movement of air past the device to be cooled to carry away unwanted heat generated by the device. The rate of heat dissipation is significantly greater than the convection air-cooling scheme, all other variables held equal.
Forced air-cooling of ion laser devices is ideally accomplished with the air blown axially along the length of the laser tube. This axial flow method has an advantage over a transverse flow system in that a uniform temperature can be maintained along a cross-section of the laser tube at operating equilibrium. If all portions of the tube around the circumference are maintained at the same temperature, mirror instability problems and tube breakage caused by non-uniform temperature gradients associated with transverse-flow forced air-cooling are prevented.
In some applications, axial-flow forced air-cooling is impractical. In such instances, transverse-flow forced air-cooling may be used almost as effectively, provided that temperature gradient of transverse air flow is dealt with effectively.
It is well known to make a heat-dissipating fin assembly for a laser by brazing transversely-oriented fins onto a metallic sleeve and, in turn, brazing the sleeve onto the ceramic bore of the laser tube. While the resulting structure has been found to be usable, it creates several problems. One problem is that stability of the laser cavity forming mirror is degraded due to differential thermal expansion during device warm-up, since the metallic sleeve to which the fins are mounted has a different coefficient of thermal expansion than does the ceramic bore which it surrounds. Another problem is that device warm-up time can be relatively lengthy because the sleeve mounting the fin represents an additional thermal mass. Therefore, there exists a need in the art for a transverse-flow forced air-cooling system for ion gas lasers which allows better heat transfer, more efficient heat dissipation, promotes a shorter warm-up time, permits a greater amount of internal power generated, and avoids or minimized mirror instability.